Add strain (#72)

* Add `strain`

config.json

@@ -405,6 +405,14 @@
         "prerequisites": [],
         "difficulty": 1
       },
+      {
+        "slug": "strain",
+        "name": "Strain",
+        "uuid": "9a7c65ae-14c1-41d2-bb4a-f46d74a158e1",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "sum-of-multiples",
         "name": "Sum of Multiples",

exercises/practice/strain/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Implement the `keep` and `discard` operation on collections.
+Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
+
+For example, given the collection of numbers:
+
+- 1, 2, 3, 4, 5
+
+And the predicate:
+
+- is the number even?
+
+Then your keep operation should produce:
+
+- 2, 4
+
+While your discard operation should produce:
+
+- 1, 3, 5
+
+Note that the union of keep and discard is all the elements.
+
+The functions may be called `keep` and `discard`, or they may need different names in order to not clash with existing functions or concepts in your language.
+
+## Restrictions
+
+Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/strain/.meta/config.json

@@ -0,0 +1,22 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "contributors": [
+    "chunes3"
+  ],
+  "files": {
+    "solution": [
+      "src/strain.art"
+    ],
+    "test": [
+      "tests/test-strain.art"
+    ],
+    "example": [
+      ".meta/src/example.art"
+    ]
+  },
+  "blurb": "Implement the `keep` and `discard` operation on collections.",
+  "source": "Conversation with James Edward Gray II",
+  "source_url": "http://graysoftinc.com/"
+}

exercises/practice/strain/.meta/src/example.art

@@ -0,0 +1,18 @@
+keep: function [values :block fn :literal][
+    f: var fn!
+    fold.seed:[] values [acc value] [
+        print value
+        switch (f value)
+            -> insert acc size acc value
+            -> acc 
+    ]
+] 
+
+discard: function [values :block fn :literal][
+    f: var fn!
+    fold.seed:[] values [acc value] [
+        switch (not? f value)
+            -> insert acc size acc value
+            -> acc 
+    ]
+]

exercises/practice/strain/.meta/tests.toml

@@ -0,0 +1,52 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[26af8c32-ba6a-4eb3-aa0a-ebd8f136e003]
+description = "keep on empty list returns empty list"
+
+[f535cb4d-e99b-472a-bd52-9fa0ffccf454]
+description = "keeps everything"
+
+[950b8e8e-f628-42a8-85e2-9b30f09cde38]
+description = "keeps nothing"
+
+[92694259-6e76-470c-af87-156bdf75018a]
+description = "keeps first and last"
+
+[938f7867-bfc7-449e-a21b-7b00cbb56994]
+description = "keeps neither first nor last"
+
+[8908e351-4437-4d2b-a0f7-770811e48816]
+description = "keeps strings"
+
+[2728036b-102a-4f1e-a3ef-eac6160d876a]
+description = "keeps lists"
+
+[ef16beb9-8d84-451a-996a-14e80607fce6]
+description = "discard on empty list returns empty list"
+
+[2f42f9bc-8e06-4afe-a222-051b5d8cd12a]
+description = "discards everything"
+
+[ca990fdd-08c2-4f95-aa50-e0f5e1d6802b]
+description = "discards nothing"
+
+[71595dae-d283-48ca-a52b-45fa96819d2f]
+description = "discards first and last"
+
+[ae141f79-f86d-4567-b407-919eaca0f3dd]
+description = "discards neither first nor last"
+
+[daf25b36-a59f-4f29-bcfe-302eb4e43609]
+description = "discards strings"
+
+[a38d03f9-95ad-4459-80d1-48e937e4acaf]
+description = "discards lists"

exercises/practice/strain/src/strain.art

@@ -0,0 +1,7 @@
+keep: function [values :block fn :literal][
+    panic "Please implement the keep function"
+] 
+
+discard: function [values :block fn :literal][
+    panic "Please implement the discard function"
+]

exercises/practice/strain/tester.art

@@ -0,0 +1,3 @@
+import.version:1.1.2 {unitt}!
+
+runTests.failFast findTests "tests"

exercises/practice/strain/tests/test-strain.art

@@ -0,0 +1,129 @@
+import.version:1.1.2 {unitt}!
+import {src/strain}!
+
+suite "Strain" [
+    test "keep on empty list returns empty list" [
+        values: []
+        predicate: $[x] -> true
+        results: keep values 'predicate
+        expected: []
+        assert -> expected = results
+    ]
+
+    test.skip "keeps everything" [
+        values: [1 3 5]
+        predicate: $[x] -> true
+        results: keep values 'predicate
+        expected: [1 3 5]
+        assert -> expected = results
+    ]
+
+    test.skip "keeps nothing" [
+        values: [1 3 5]
+        predicate: $[x] -> false
+        results: keep values 'predicate
+        expected: []
+        assert -> expected = results
+    ]
+
+    test.skip "keeps first and last" [
+        values: [1 2 3]
+        results: keep values 'odd?
+        expected: [1 3]
+        assert -> expected = results
+    ]
+
+    test.skip "keeps neither first nor last" [
+        values: [1 2 3]
+        results: keep values 'even?
+        expected: [2]
+        assert -> expected = results
+    ]
+
+    test.skip "keeps strings" [
+        values: ["apple" "zebra" "banana" "zombies" "cherimoya" "zealot"]
+        predicate: $[x] -> prefix? x "z"
+        results: keep values 'predicate
+        expected: ["zebra" "zombies" "zealot"]
+        assert -> expected = results
+    ]
+
+    test.skip "keeps lists" [
+        values: [[1 2 3]
+                 [5 5 5]
+                 [5 1 2]
+                 [2 1 2]
+                 [1 5 2]
+                 [2 2 1]
+                 [1 2 5]]
+        predicate: $[x] -> contains? x 5
+        results: keep values 'predicate
+        expected: [[5 5 5]
+                   [5 1 2]
+                   [1 5 2]
+                   [1 2 5]]
+        assert -> expected = results
+    ]
+
+    test.skip "discard on empty list returns empty list" [
+        values: []
+        predicate: $[x] -> true
+        results: discard values 'predicate
+        expected: []
+        assert -> expected = results
+    ]
+
+    test.skip "discards everything" [
+        values: [1 3 5]
+        predicate: $[x] -> true
+        results: discard values 'predicate
+        expected: []
+        assert -> expected = results
+    ]
+
+    test.skip "discards nothing" [
+        values: [1 3 5]
+        predicate: $[x] -> false
+        results: discard values 'predicate
+        expected: [1 3 5]
+        assert -> expected = results
+    ]
+
+    test.skip "discards first and last" [
+        values: [1 2 3]
+        results: discard values 'odd?
+        expected: [2]
+        assert -> expected = results
+    ]
+
+    test.skip "discards neither first nor last" [
+        values: [1 2 3]
+        results: discard values 'even?
+        expected: [1 3]
+        assert -> expected = results
+    ]
+
+    test.skip "discards strings" [
+        values: ["apple" "zebra" "banana" "zombies" "cherimoya" "zealot"]
+        predicate: $[x] -> prefix? x "z"
+        results: discard values 'predicate
+        expected: ["apple" "banana" "cherimoya"]
+        assert -> expected = results
+    ]
+
+    test.skip "discards lists" [
+        values: [[1 2 3]
+                 [5 5 5]
+                 [5 1 2]
+                 [2 1 2]
+                 [1 5 2]
+                 [2 2 1]
+                 [1 2 5]]
+        predicate: $[x] -> contains? x 5
+        results: discard values 'predicate
+        expected: [[1 2 3]
+                   [2 1 2]
+                   [2 2 1]]
+        assert -> expected = results
+    ]
+]